1. Field of the Invention
The present invention relates to a ceramic electronic part and producing method thereof, and particularly, to a ceramic electronic part having an external electrode on the outer face of a ceramic chip such as a laminated capacitor, a chip coil or a resistor, and to a method for producing of the ceramic electronic part.
2. Description of the Prior Art
A laminated capacitor which is an example of a conventional ceramic electronic part, is the laminated capacitor having external electrodes on an outer surface of a ceramic molded product which has a plurality of internal electrodes, wherein the external electrodes are connected to the internal electrodes. When manufacturing the laminated capacitor, first, a plurality of ceramic green sheets onto which a conductive paste for serving as an internal electrode is printed, are laminated, pressed and cut into any size to form a laminate. The laminate is baked into a ceramic chip, which is coated with a conductive paste on outer surfaces thereof and baked to form an external electrode.
In this case, in order to improve the solderability and soldering heat resistance of the external electrode, the ratio of silver, palladium etc. in the conductive paste and the addition of glass frit are controlled.
As a method of forming the external electrode, a thin-film forming process such as sputtering or an electrolytic plating process is used to form the external electrode with a multi-layer structure such as nickel, tin and solder.
A method of forming the external electrode simultaneously with sintering the laminate onto which a conductive paste containing the glass frit is coated is disclosed in Japanese Patent Publication No. 40842/1987.
In the method of forming the baked external electrode on the ceramic chips the ceramic chips must be aligned when coating the conductive paste or when masking at in the sputtering process. However, the ceramic chips are so small that they are difficult to align.
An additional problem is that sintering of the laminate may cause deformation of the ceramic chips such as a bend or a warp. Therefore, some of the ceramic chips can not be handled with a machine for automated forming of the external electrode, which results in a low yield and causes difficulty in reducing the cost at mass production.
Moreover, in the method of forming the external electrode on the ceramic chip by electrolytic plating, the weatherability is deteriorated by a plating liquid permeated into the ceramic chip, spoiling reliability of the parts.
In the electronic parts having the external electrode formed on the outer surface of the ceramic chip by these methods, for example, when external circuits are to be soldered, the external electrode may elute into the solder to cause poor heat resistance.
In the method disclosed in Japanese Patent Publication No. 40842/1987, the bonding strength between the ceramic chip and the external electrode is strengthened by the glass frit, whereby the elution of the external electrode into the solder is prevented. However, when the laminate is baked, the glass frit diffuses into the laminate to produce stresses inside the ceramics, so that a bend, warp or crack is produced, which results in poor productivity.